A control method and a control arrangement for an adjusting device is disclosed in British Patent 2,007,878. In this arrangement, an actuating device is so adjusted for control purposes that the operating variable to be controlled corresponds to a pregiven desired value. In this case, the operating variable is the idle engine speed. The drive of the actuating device takes place via a clocked drive signal having a fixed frequency with variable pulse width or variable pulse-duty factor.
Actuating devices of this kind are as a rule burdened with a hysteresis with respect to their drive performance. This hysteresis occurs because of slip and friction characteristics or is based on the magnetic remanence of the rotor. Furthermore, regions can occur while driving through the entire actuating range of the actuating device which are characterized by a jump-like performance of the actuator position with reference to the drive signal variable or, within these regions, no defined relationship can be present between the drive signal variable and the actuator position. For this reason, limitations must be accepted with respect to the precision of the drive of such an actuating device.